1. Field of the Invention
The present invention relates to a cooling system for an internal combustion engine, in which a ring is integrated around a plurality of fan blades.
2. Description of the Prior Art
A typical cooling fan includes a boss 1 coupled to an input member, and a plurality of fan blades projecting radially outwardly from the outer periphery of the boss 1 as shown in FIGS. 12 and 13. There are a few disadvantages to this arrangement. First, cool air passes through a clearance 4 between the tips of the blades 2 and a shroud 3 as best seen in FIG. 12. This counterflow of air A causes a reduction in the volume of cool air. Secondly, a spiral flow of air B is created around the tips of the blades 2 as best seen in FIG. 13. This results in the occurrence of undesirable noise.
Japanese utility model laid-open publication No. 52/11203 discloses an improved cooling system wherein a cooling fan is surrounded by a ring 5 (see FIG. 14). The disclosed cooling system, particularly those illustrated in FIGS. 15(A) and 15(B), is easy to manufacture and install. In this system, the ring 5 has a small curvature from a cylindrical portion to a portion of maximum diameter, the maximum diameter portion being 1.0 to 1.3 times greater than the diameter of the cylindrical portion. Also, the shroud 3 overlaps the cooling fan, with or without a ring, by half of, or equal to the axial width of the fan.
Various attempts have also been made to reduce the noise. See, for example, Japanese utility model publication No. 60/21518, Japanese patent laid-open publication No. 56/56926 and Japanese utility model laid-open publication No. 50/58305. Rings mounted on cooing fans of these prior cooling system are in bellmouth form. It has been found that such a bellmouth-shaped ring is more effective in reducing the noise than those stated in the preceding paragraphs. It is apparent, however, that with such bellmouth-shaped ring , it is necessary to increase the size of a radiator by 15 to 20%.
In the design of a cooling system, a radiator is first so sized as to dissipate a substantial amount of heat. Then, a specific type of cooling fan is implemented to provide a substantial flow of air through the radiator. With the size of the radiator fixed, a fan with a ring of a bellmouth form is 10 to 20% smaller in diameter than a fan with ring in general form. It has experimentally found that the former provides a flow of air only 58 to 77% of that of the latter. In order for the former to provide as much a flow of air as the latter, rotational number of the former must be 1.3 to 1.7 times greater than that of the latter. However, this results in a substantial increase in the noise. It should also be noted that mounting of the former to a vehicle body is cumbersome.